Systematic Patterns in Land Precipitation over the Maritime Continent due to Land-Sea Contrast during MJO Propagation

Abstract:

The land-sea contrast in the Maritime Continent (MC) has been found to influence the Madden-Julian Oscillation (MJO). However, the specific contribution from individual islands to the precipitation over the surrounding islands during MJO propagation is not well known. We found that when an island is removed in the presence of lower-tropospheric westerlies, precipitation increases (decreases) over islands that are located to its east (west) due to the strengthening (weakening) of the westerlies. Frictional convergence of the stronger westerlies, aided by Coriolis, leads to an increase in vertical advection of moisture and precipitation over an island located to the east. On the other hand, the reduced heating over the removed island reduces the westerlies to the west of the removed island and is consistent with the theory. During background easterlies prior to MJO arrival, no systematic pattern of precipitation was found. The results imply that changes in large-scale circulation in response to convection over neighboring islands may also influence its precipitation. Therefore, biases in model precipitation over an island in the MC during the westerly phase of the MJO may arise from bias in precipitation over a neighboring island.